One of the known secondary batteries has a laminated film, which is a metal layer with a surface thereof laminated with a synthetic resin layer, used as an exterior body, has a power generation element including a plurality of stacked positive electrode plates, negative electrode plates, and separators housed therein together with an electrolyte solution, and has a flat shape (for example, Patent Literature 1).
A known example of a terminal (a terminal of a positive or negative electrode) for extracting current out of the power generation element inside this type of secondary battery is a terminal including a nickel layer formed on a surface of a terminal main body including a conductive material such as copper (for example, a nickel plated layer). For sealing the exterior body with the power generation element and the like housed therein, the terminal to be applied is held by the exterior body and the held portion is sealed.
The sealing of the held portion is conducted by a known method as below. In this method, a heat-seal resin layer is formed in advance in the portion where the terminal surface (nickel layer surface) is held. Through the resin layer, the terminal is held by the exterior body. The held portion is then heat-sealed. In another known method, an anticorrosive layer is formed to cover the surface of the nickel layer in the terminal, which will be in contact with the electrolyte solution in the exterior body, for preventing the corrosion, the elusion, and the like due to the contact with the electrolyte solution. It is considered that the force of peeling due to the internal pressure in the exterior body operates on the held portion.
An object of the present invention is to provide a secondary battery with higher reliability while improving the peeling strength between the terminal and the exterior body.